What is the standard testing distance for a Snellen chart?

The standard testing distance for a Snellen chart is 20 feet. This distance is traditionally used in clinical settings to provide a consistent and standardized way of measuring visual acuity. The Snellen chart displays letters of varying sizes, and testing at 20 feet allows eye care professionals to accurately evaluate how well a patient can see at that standard distance.

By using this specific measurement, practitioners can effectively interpret the results against established norms. The Snellen fraction represents the smallest line of letters that a person can read at a distance of 20 feet compared to what a person with normal vision would see at that same distance. For instance, a result of 20/20 vision means that a person can read at 20 feet what should normally be seen at that distance.

Testing at other distances, such as 10, 15, or 25 feet, would require adjustments in the interpretation of visual acuity results and could lead to inconsistencies in how visual capabilities are assessed. Thus, 20 feet remains the recognized standard distance for Snellen chart evaluations in eye care practices.